US20060106270A1 relates to a process wherein the average propylene cycle selectivity of an oxygenate to propylene (OTP) process using a dual-function oxygenate conversion catalyst is substantially enhanced by the use of a combination of: 1) moving bed reactor technology in the hydrocarbon synthesis portion of the OTP flow scheme in lieu of the fixed bed technology of the prior art; 2) a hydrothermally stabilized and dual-functional catalyst system comprising a molecular sieve having dual-function capability dispersed in a phosphorus-modified alumina matrix containing labile phosphorus and/or aluminum anions; and 3) a catalyst on-stream cycle time of 400 hours or less. The use of a mixture of a zeolitic catalyst system with a non-zeolitic catalyst system is described. This mixed catalyst embodiment can be accomplished either using a physical mixture of particles containing the zeolitic material with particles containing the non-zeolitic material or the catalyst can be formulated by mixing the two types of material into the phosphorus modified aluminum matrix in order to form particles having both ingredients present therein. In either case the preferred combination is a mixture of ZSM-5 or ZSM-11 with SAPO-34 in relative amounts such that ZSM-5 or ZSM-11 comprises 30 to 95 wt % of the molecular sieve portion of the mixture with a value of about 50 to 90 wt % being especially preferred.
US20060063956A1 relates to a process wherein the average cycle propylene selectivity of an oxygenate to propylene (OTP) process using one or more fixed or moving beds of a dual-function oxygenate conversion catalyst with recycle of one or more C4+ olefin-rich fractions is substantially enhanced by the use of selective hydrotreating technology on these C4+ olefin-rich recycle streams to substantially eliminate detrimental coke precursors such as dienes and acetylenic hydrocarbons. This hydrotreating step helps hold the build-up of detrimental coke deposits on the catalyst to a level which does not substantially degrade dual-function catalyst activity, oxygenate conversion and propylene selectivity, thereby enabling a substantial improvement in propylene average cycle yield. The propylene average cycle yield improvement enabled by the present invention over that achieved by the prior art using the same or a similar catalyst system but without the use of the hydrotreating step on the C4+ olefin-rich recycle stream is of the order of about 1.5 to 5.5 wt-% or more. The preferred combination is a mixture of ZSM-5 with SAPO-34 in relative amounts such that SAPO-34 comprises 30 to 70 wt % of the molecular sieve portion of the mixture with a value of about 45 to 55 wt % being especially preferred.
U.S. Pat. No. 6,051,746 describes oxygenate conversions using modified small pore molecular sieve catalysts. The invention relates to a process for converting oxygenated organic material, to olefins using small pore molecular sieve catalysts. More particularly, the invention relates to a method for converting oxygenated organic material to olefins with improved the olefin yields and decreased yields of methane and other light saturate byproducts. The improved yield slate is achieved by treating the small pore molecular sieve catalyst with a modifier selected from the group consisting of polynuclear aromatic heterocyclic compounds with at least three interconnected ring structures having at least one nitrogen atom as a ring substituent, each ring structure having at least five ring members, decomposed derivatives of said polynuclear aromatic heterocyclic compound, and mixtures thereof.
US20060195001A1 describes combinations of molecular sieve catalysts to provide a catalyst mixture having a beneficial combination of the activities and selectivities of the individual molecular sieves. The molecular sieve catalysts can be formulated or unformulated silicoaluminophosphate molecular sieves, silicoaluminate molecular sieves, and/or metalloaluminophosphate molecular sieves. In particular, said application relates to mixtures of molecular sieves for use as catalysts in converting oxygenates such as methanol to olefins. At [0113] and [0114] on page 10 are described mixtures of SAPO-34 and AEI/CHA intergrowth material having a Si:Al ratio of roughly 0.06. As explained in [0065] AEI and CHA are respectively the structure of SAPO-18 and SAPO-34.
U.S. Pat. No. 6,951,830B2 relates to a catalyst composition, a method of making the same and its use in the conversion of a feedstock, preferably an oxygenated feedstock, into one or more olefin(s), preferably ethylene and/or propylene The catalyst composition comprises a molecular sieve, such as a silicoaluminophosphate and/or an aluminophosphate, hydrotalcite, and optionally a rare earth metal component.
US20070043250A1 describes an oxygenate conversion catalyst useful in the conversion of oxygenates such as methanol to olefinic products which is improved by the use of a catalyst combination based on a molecular sieve in combination with a co-catalyst comprising a mixed metal oxide composition which has oxidation/reduction functionality under the conditions of the conversion. This metal oxide co-catalyst component will comprise a mixed oxide of one or more, preferably at least two, transition metals, usually of Series 4, 5 or 6 of the Periodic Table, with the metals of Series 4 being preferred, as an essential component of the mixed oxide composition. The preferred transition metals are those of Groups 5, especially titanium and vanadium, Group 6, especially chromium or molybdenum, Group 7, especially manganese and Group 8, especially cobalt or nickel. Other metal oxides may also be present. The preferred molecular sieve components in these catalysts are the high silica zeolites and the SAPOs, especially the small pore SAPOs (8-membered rings), such as SAPO-34. These catalyst combinations exhibit reduced coke selectivity have the potential of achieving extended catalyst life. In addition, these catalysts have the capability of selectively converting the hydrogen produced during the conversion to liquid products, mainly water, reducing the demand on reactor volume and product handling.
Small pore silicoaluminophosphate (SAPO) molecular sieve catalysts have excellent selectivity in oxygenates to light olefin reactions. However, these catalysts have a tendency to deactivate rapidly during the conversion of oxygenates to olefins and the ratio C3/C2 could be improved. Therefore a need exists for methods to decrease the rate of deactivation of small pore zeolitic catalysts during such conversions and to improve the C3/C2 ratio.
It has been discovered that addition of a small amount of medium or large pore crystalline silicoaluminate, silicoaluminophosphate materials or silicoaluminate mesoporous molecular sieves to a small pore MeAPO molecular sieve based catalyst leads to substantial increase of C3/C2 ratio, C4+ yield and stability in XTO than was obtained over parent molecular sieve (MeAPO).
Higher stability of blended catalysts provides a possibility to operate at higher flow rate, increase the catalyst on-stream time in XTO conversion reactor and decrease the size of regeneration section or the frequency of regeneration. (on-stream time is the time that a catalyst resides in the conversion reactor and exhibits still sufficient catalytic activity, before it has to be taken off-line for regeneration or replacement)
Unexpectedly, this blended catalysts possesses reduced coke selectivity in comparison with the weighted average of the individual molecular sieves.
The excess of C4+ as well as ethylene can be converted to propylene in an olefin cracking fixed bed reactor (OCP) in combination with the XTO process. Ethylene can be recycled back in XTO reactor or to the OCP reactor. The excess C4+ as well as the ethylene can be converted to more propylene by recycling C4+ and ethylene back to the XTO reactor. The catalyst blend allows the conversion of organic compounds, C4+ and ethylene at the same time.
Stated above small pore MeAPO molecular sieves contain 8 members ring as a largest pore aperture in the structure, medium pore crystalline silicoaluminates contain 10 members ring as a largest pore aperture, large pore crystalline silicoaluminates contain 12 members ring in the structure. Stated above medium, large pore and mesoporous molecular sieves have acid properties and could catalyse the formation of aromatic precursor from used feedstock.
In the XTO process the ethylene, propylene and higher hydrocarbons are formed via a “carbon pool” mechanism. Ethylene, propylene and C4+ olefins selectivities in XTO process are related to the number of methyl groups attached to benzene rings trapped in the nanocages. The product spectrum varies strongly with the pore size of the catalytic material (shape selectivity), and when the small pore SAPO-34 (chabasite structure) is used as catalyst the hydrocarbon products are mostly ethene and propene, and some substantially linear butenes, the only product molecules small enough to escape with ease through the narrow pores.
It has been discovered that medium or large pore crystalline silicoaluminate, silicoaluminophosphate materials or silicoaluminate mesoporous molecular sieves play a role of a faster in-situ supply for aromatics precursor for olefins production by carbon pool mechanism. One object of this invention is in-situ on-purpose formation of some additional organic reaction centers by adding to the MeAPO a small amount of acid co-catalyst with larger pore opening than the MeAPO. These materials are capable to produce a small amount of higher molecular weight precursors that can enter into the pore system of the small pore MeAPO where they are converted into the aromatics under XTO conditions. These aromatics constitute the active centers for XTO according to the carbon pool mechanism. These aromatics are trapped by MeAPO micro porous system in a more optimum way without formation of a lot of coke by-products. This allows increasing of catalyst stability and C3/C2 ratio.
Without being bonded by an explanation, inventors think that an optimum concentration of the methylbenzenes organic reaction centers leads to higher light olefins production and to a slower deactivation. However the olefins production is limited by diffusion of heavy olefins out of the micropore system of MeAPO in which usually methylbenzenes are trapped. Formation of the methylbenzenes inside of MeAPO pore system requires a certain time and is accompanied by coke formation. More coke formation in the small pore MeAPO reduces the accessible pore volume and results in faster loss of catalytic activity.